It is known that the compound A and/or the compound B has/have the following chemical structure, has/have an action of inhibiting a specific potassium channel (BEC1 potassium channel) and an anti-depression action, and is/are useful for treatment of dementia (U.S. Pat. No. 7,375,222, herein incorporated by reference).

Specifically, the compound A is isolated in the composition of compound A.2 HCl.0.3H2O.0.1 ethyl acetate (U.S. Pat. No. 7,375,222, herein incorporated by reference), but there is no specific report on other pharmaceutically acceptable acid addition salts. Further, the compound B is described only as paper Examples (U.S. Pat. No. 7,375,222, herein incorporated by reference).